1. Field of the Invention
This invention relates to an image forming apparatus such as a color copying machine for forming a duplicate image of a color image, for example.
2. Description of the Related Art
Generally, color originals are roughly divided into three types depending on the printing rate. The three types are photographs and printed matters represented by natural pictures having a printing rate of 50% or more, presentation materials mainly including graphs and diagrams and having a printing rate of a few ten %, and general documents mainly including letters and tables and having a printing rate of approx. 10%.
Conventionally, only the photographs and printed matters are obtained as color originals at hand, but now, with the advent of color personal computers and color printers, presentation materials are presented in a colored form, and color printing is started to be used to represent the letter emphasis and ruled lines owing to a reduction in the cost of the above color OA instruments. Therefore, the printing rate of color originals is rapidly reduced.
Among color copying machines for copying color originals, an electrophotographic type becomes dominant because of the operation speed is high and the number of sheets to be copied for each minute can be recorded. In this case, a charge amount charged on the user is determined by the price for one sheet and is independent of the degree of the printing rate. This is because the electrophotographic copying machine has been widely used to deal with monochromatic letter originals having a low printing rate (several %), the service life of the optical semiconductor drum which is a consumable part is short and the cost thereof occupies a large part of the running cost, and the charge amount is not so much dependent on the amount of toner consumption. Further, the color copying machine dealing with color originals has substantially a high printing rate and the running cost thereof is set to a value several ten times that of the monochromatic copying machine since the total demand for color toner is little.
Thus, in the color copying machine of electrophotographic type having a sufficiently high performance as a color copying machine and having a high recording speed, the copying charge for one sheet is set at a preset price for both of a color original having a high printing rate and a color original having a low printing rate irrespective of the printing rate of the color original. Therefore, in a case where a color original having a low printing rate is copied, a charge amount higher than the actual running cost may be set and charged on the user.
Further, like the monochromatic copying machine, in the color copying machine, the service maintenance is effected at regular intervals, or for every preset number of copying sheets. The color copying machine uses toners of four colors and the image forming process includes four stages, but the frequencies at which the toners are used become greatly different according to the type of original and the type of original is different for each user, and as a result, the amounts of toners tend to become short or excessive if the service maintenance is always equally effected. Therefore, there occurs a problem that useless or insufficient maintenance is effected.
Further, there occurs a problem that even if the record of usage of the recording material by a plurality of users is stored in a memory or the like, the record of usage cannot be used as the maintenance guide, for example, if it is not adequately modified.